The periodic table Flashcards
Robert Boyle
Irish scientist who defined the element
element
a substance which cannot be broken down into simpler substances by chemical means, e.g. carbon
Humphry Davies
Isolated elements by electrolysis (passing electricity through substances) e.g. sodium from NaOH
Johann Dobereiner
First to note a relationship between the weights and properties of elements (triads).
Triad
A group of there elements of similar chemical properties, in which the weight of the middle element is approximately equal to the average of the two others,
e.g. Cl, Br, I.
Newland’s Law of Octaves
Properties of elements repeat every eight elements when arranged in order of increasing atomic weight.
- Discrepancies as he tried to force a pattern instead of leaving gaps for yet to be discovered elements.
Mendeleev’s Periodic Law
When elements are arranged in order of increasing atomic weights, properties of the elements repeat periodically.
Mendeleev’s Periodic table
- In order of atomic weight
- No noble gases
- No D-block
- Gaps for yet to be discovered elements
Henry Moseley
Used x-rays to determine the number of protons in an atom (atomic number)
Showed elements should be arranged by atomic number not mass
Modern Periodic Law
when elements are arranged by atomic number, properties of elements repeat periodically
Atomic number
Number of protons present in the nucleus of an atom
Mass number
Number of protons and neutrons in the nucleus of an atom
Isotopes
Atoms with the same number of protons but different numbers of neutrons.
e.g. protium, deuterium, tritium
Relative Atomic mass
the average mass of isotopes of an element, taking their abundances into account, presented on a scale where atoms of the carbon-12 isotope have a mass of exactly 12
